Dialysis of the blood or hemodialysis is a well known and accepted medical technique. For example, kidney malfunction or failure requires that kidney function be performed artificially, as through hemodialysis.
Successful hemodialysis involves the removal of waste materials and excess water. The removal of waste materials is effectively accomplished through prior art hemodialysis systems which may also compensate, through replacement, for the removal of too much of a particular blood constituent, glucose, for example. The controlled removal of excess water, on the other hand, has proven to be a major problem in hemodialysis. Excess water is removed by ultrafiltration which is established by maintaining the dialysate pressure within the dialyzer lower than that of the blood pressure. Prior art hemodialysis systems have established this pressure condition and monitored it through the use of pressure gauges on the dialysate side. However, these prior art systems have been unable to even estimate the ultrafiltration rate with any accuracy.
The removal of too much water too fast will cause a hemodialysis patient to go into shock. Because the ultrafiltration rate cannot accurately be determined for prior art hemodialysis systems, those systems have been operated at very low ultrafiltration rates. This has been one factor underlying the extremely long time of dialysis.
One solution to the above mentioned difficulty in establishing ultrafiltration rate with prior art hemodialysis systems has been to place the dialysis patient on a weighing bed to determine the amount of water removal by the decrease in patient weight. Obviously, this system has an extremely high cost and is available only in those situations where some control over, or a knowledge of, the ultrafiltration volume is absolutely necessary. Also, the weighing bed technique will not indicate the instantaneous ultrafiltration rate.